LONDON — The black-clad Islamic militant fighter filmed in the beheading of American journalist James Foley appears to be British, the UK foreign minister said Wednesday — a development that underscores the insurgents’ increasingly sophisticated use of Western fighters to mobilize recruits and terrorize enemies.

Foreign Secretary Philip Hammond said the man in the video with Foley “appears to have been a British person.”

US officials have confirmed as authentic the grisly video showing an Islamic State militant beheading Foley and threatening to kill another hostage.

The masked militant in the clip speaks fluent English with what Lancaster University linguist Claire Hardaker said sounds like a London accent.

American journalist James Foley, kneeling in orange, in a video released by the Islamic State that apparently showed him being beheaded by his captor, August 19, 2014. (screen capture: YouTube/News of the World)

Hammond told the BBC that Britain was aware that UK nationals were involved in committing atrocities with Islamic State extremists and other organizations.

Hammond says the possible involvement of a Briton underscored the risks that those now fighting with Islamic militants could return to Britain and carry out attacks at home.

British officials have said that several hundred people from Britain have traveled to Syria to join the battle against President Bashar Assad, and some may have crossed into Iraq as part of the rapid advance of the Islamic State group. French and German officials have recently put the combined total of those countries around 1,300.

Shiraz Maher of the International Center for the Study of Radicalization at King’s College London, said the video was evidence that British jihadis were “some of the most vicious and vociferous fighters” in Syria and Iraq.

“Unfortunately the British participation in the conflicts now raging in both Syria and Iraq has been has been one of full participation, one that has seen them at the front lines, taking part in the conflict in every way,” Maher told BBC radio. “So we have seen British fighters out there operating as suicide bombers, we have seen them operating as executioners.”

The group has previously used Western fighters in its recruitment videos. In June, it released a video showing British and Australian militants exhorting compatriots to join them in violent jihad.

Nigel Inkster, a terrorism expert at the International Institute for Strategic Studies, said the videos reflected an increasingly sophisticated media strategy designed to energize recruits and deliver to Western governments and citizens a message “of fear and a perception of inevitability.”